The present invention relates to a tool holder robot permitting all types of interventions or operations within a closed enclosure having an access opening. It aims more particularly at permitting maintenance and repairs to water boxes of steam generators of pressurized light water nuclear power stations.
The water box of a steam generator is constituted in certain existing cases by a hemispherical enclosure defined by a diametral plane formed by the tubular plate of the exchanger arranged horizontally in the upper part. The water box is vertically subdivided into a hot half-box and a cold half-box by a vertical partition passing through the median plane of the hemisphere. Each water half-box thus forms a closed enclosure shaped like a quarter sphere on which is provided at least one substantially cylindrical access opening oriented in accordance with a radius of the sphere.
Each access opening is called a manhole and has dimensions enabling an operator to enter the enclosure after emptying, when work has to be carried out therein. The manhole is located in the bottom part of the steam generator. The inclination of the opening axis is approximately 45.degree. relative to the vertical. When the steam generator is operating normally, the manhole is closed by a cover studded or pinned to a circular flange defining the manhole. Various types of operation are carried out within water boxes.
It is firstly necessary to regularly decontaminate the inner walls of half-boxes, which are superficially highly contaminated with radiating elements. This decontamination makes it possible to improve the working conditions of personnel having to work both within half-boxes where very high radiation levels prevail and outside the same, particularly in the vicinity of the manhole. The decontamination processes to be put into operation are either of a chemical or a mechanical nature (pressurized water sandblasting).
During each operational shutdown, there is a systematic inspection of the state of the tubes of each generator using various processes, one consisting of checking each tube by introducing an eddy current probe into it. This systematic inspection aims at inspecting any deterioration which may have occurred during operations, such as cracking of tubes, constriction thereof due to corrosion to intermediate spacer plates, blocking of tubes, etc. The leaking or defective tubes then have to be repaired or sealed, which requires the use of numerous difficulty employable tools in view of the environment in question.
It is also useful to be able to inspect and repair the actual tubular plate, which can be damaged by migrating substances transported by the water of the primary circuit.
All the operations to be carried out within enclosures which are highly contaminated with radiating elements lead to significant dangers for the personnel involved, which are exposed to high radioactive radiation.
In order to minimize or eliminate human interventions, a number of solutions have been proposed, which can be grouped into two equipment categories.
First category: remotely controlled devies for intervening on tubes.
A large number of operations to be carried out on tubes were performed manually by an operator who on a number of occasions had to enter the tube for fitting the tools to the tubular plate. A first tool holder device known as a "spider" made it possible to mechanize the movements of the tools on the tubular plate. However, the spider has to be fitted by an operator, who also has to change the tools and detach the spider at the end of the operation. Moreover, the spider only moves very slowly and has a limited operating efficiency, particularly in the case where the tubes are blocked and the spider cannot be fixed to them. Finally, as the location of the spider can only be defined by counting the number of passes made, it is not possible to carry out an absolute marking of the position of the inspected tube.
Another tool holder type for fixing to the plate was proposed in French Patent Application No. 2 211 721. Although this tool holder type has certain advantages compared with the spider, such as absolute marking of the tubes, fast movements and the possibility of fitting several types of tool, it still has important disadvantages, such as its overall dimensions, the obscuring of a row of tubes on which it is possible to intervene and the need for entry of personnel for its fitting and removal.
French Patent Application No. 2 394 374 also discloses a device for fitting a spider-type tool holder in order to reduce the number of times personnel must enter water boxes. This device makes it possible to place the spider on the tubular plate from the outside and then remove it. However, this presupposes the prior fitting in a manual manner of a fixed guidance mast within the box.
Other spider holder devices suffering from the same disadvantages are e.g. disclosed in U.S. Pat. No. 3 913 752.
Second category: remotely controlled devices for intervening on all the elements constituting a water half-box.
These devices have essentially been developed to permit mechanical decontamination and consequentially must not only be able to reach the tubular plate but also the separating partition and the inner wall of the spherical bowl.
A first type of device proposed consists of an arm, whereof one end is articulated by a spherical joint to a plate fixed in the vicinity of a centre of the sphere to the tubular plate. A tool-holder carriage or the like is slidingly mounted on the arm and carries a fixed orientation decontamination nozzle. However, this device still requires the intervention of personnel for its fitting within the water box, as well as the intervention of an operator in front of the manhole for modifying the orientation of the decontamination nozzle during a change of surface to be swept. In this device also hides that portion of the tubular plate corresponding tubes positioned beneath its anchoring plate.